This application is a national stage entry under 35 U.S.C. xc2xa7 371 from International Application No. PCT/EP98/00011, filed Jan. 2, 1998, in the European Patent Office; additionally, Applicant claims the right of priority under 35 U.S.C. xc2xa7 119(a)-(d) based on patent application No. 197 00 101.7, filed Jan. 3, 1997, in the German Patent Office; the contents of both of which are relied upon and incorporated herein by reference.
The invention relates to a tread pattern for a vehicle tire including at least one circumferentially extending longitudinal groove and, emanating from the longitudinal groove, transverse grooves for defining blocks in the pattern and sipes arranged in the tread, the sipe depth extending from the pattern face in the direction of the pattern base.
In the case of such a pattern configuration the longitudinal grooves (extending circumferentially) dictate the side stability and prevent aquaplaning of such a tire. The transverse grooves (extending axially) have the task of a better transfer of driving, cornering and braking forces, whereby the transverse grooves may be oriented perpendicular or slanting to the circumferentially extending longitudinal groove. The sipes provided additionally in the tread of the tread pattern are necessary in increasing the number of traction edges and thus to improve the traction and braking response by positive contact.
Employing conventional sipes in the tread of the tread pattern of a tire is hampered by a number of disadvantages. Sipes configured as narrow cuts in the blocks of the tread pattern thus result in a reduction in stiffness of the individual blocks, as a result of which the individual blocks have a greater mobility involving drawbacks in tire handling and ride, especially in dry, wet and also snow-bound pavement conditions. In getting round such disadvantages it has hitherto been necessary to compensate inadequate block stiffness by specifically engineering the number, array and depth of the sipes which is, however, difficult and complicated and results in complicated tread patterns. This, last but not least, results in tire production costs being increased.
The present invention is based on the object of sophisticating a tread pattern for vehicle tires of the aforementioned kind such that the drawbacks cited in prior art are obviated. More particularly, the intention is to define a tread pattern for a vehicle tire which despite the use of sipes ensures a sufficiently high stiffness of the individual blocks of the pattern.
To achieve this object it is provided for in accordance with the invention that at least one of the sipes disposed in at least one of the blocks is configured V-shaped.
Due to this configuration of the sipes, a tread pattern is defined which features particularly good traction and braking response. This tread pattern additionally ensures an adequate stiffness of the individual blocks when stressed by transverse forces, so that the drawbacks pertinent to the prior art in tire handling and ride are obviated. Configuring the sipes in accordance with the invention achieves opening of the sipes as usual when stressed by longitudinal forces as occurring in traction or braking, as a result of which the number of traction edges is increased. When loaded by transverse forces, as occurring, for instance, in cornering, the sipes close. This results in a stiffening of the pattern base. This stiffening materializes from the fact that due to the V-shaped configuration of the sipes, the individual wedge-shaped portions of the block, separated from each other by the V-shaped sipes, are capable of mutual support. Mutual slippage of the individual parts of the blocks, as possible in the case of conventional single-line sipes, is obviated by the sipe configuration in accordance with the invention. As a result and, especially in the presence of transverse forces, blocks are defined in the pattern which have adequate stiffness, resulting in, for instance, improved ride in dry, wet, or also snow-bound pavement conditions.
In the case of the tread pattern as provided for in accordance with the invention at least one of the sipes is configured V-shaped. It is, however, possible to also provide several V-shaped sipes per block, it being of advantage to provide a differing number of V-shaped sipes in each of the blocks when the blocks differ in length.
In one advantageous configuration of the invention the legs of the V-shaped sipe are equal in length.
In accordance with one preferred embodiment of the invention the intersection of the legs of the V-shaped sipe coincides with the side surface area of the block in which the V-shaped sipe is configured.
In accordance with another embodiment of the invention the intersection of the legs of the V-shaped sipe connects the side surface area of the block via a sipe web. In accordance with yet another embodiment of the invention it is provided for that the V-shaped sipe disposed in the block is not in contact with the side surface area of the block. Depending on the requirements on the tread pattern the individual array variants of the V-shaped sipes may be combined in the block or blocks of the pattern.
Where the V-shaped sipe is in contact with the side surface area of the block via a sipe web it can be provided for to advantage that the side surface area of the block comprises a nick in the portion connecting the sipe web.
It is of advantage when the depth of the sipe is between xc2xc and the full depth of the block.
In one advantageous aspect of the invention the at least one block comprising at least one V-shaped sipe is configured at the outer shoulder and/or inner shoulder of the tread pattern. In accordance with a further embodiment of the present invention several blocks are provided, each comprising at least one V-shaped sipe. These blocks are disposed in accordance with the invention over the full surface area of the tread pattern in a fixed or random array.
In a further aspect of the invention the free ends of the legs of the at least one V-shaped sipe are oriented towards the center line of the tread pattern.
In accordance with a further embodiment of the invention, the intersection of the legs of the at least one V-shaped sipe is oriented towards the center line of the tread pattern, it being, however, also conceivable to define a tread pattern in which [swipes] sipes are provided having both orientations, as cited above.
In yet another aspect of the invention several blocks may be provided each comprising at least one V-shaped sipe, whereby the free ends of the legs and the intersections of the legs of individual V-shaped sipes are oriented towards the center line of the tread pattern. Furthermore, orientation of the V-shaped sipes of adjacent and/or opposite blocks may be unidirectional and/or opposing and/or alternating in direction.
Due to the V-shaped sipes disposed in the blocks of the pattern in accordance with the invention a tread pattern is defined which can be manufactured simply and cost-effectively and which ensures reliable handling and ride of the tire when stressed both by longitudinal forces and transverse forces. In this arrangement, by using one or more V-shaped sipes per block, by the special array of the V-shaped sipes within the block, by orienting the sipes within the block, by varying the length of the legs of the V-shaped sipes as well as by arranging the blocks provided with the V-shaped sipes in accordance with the invention within the tread pattern a wide variety of demands made on the tire can be taken into account, this being the reason why the tread pattern in accordance with the invention can be put to use in both dry, wet and also snow-bound pavement conditions.
The tread pattern in accordance with the invention finds application preferably on a winter tire, it however also being possible to employ the tread pattern in accordance with the invention on summer and all-season tires.